In nature bluebirds evolved to
have more aggressive footholds in and on tree trunks. Providing
horizontal perches makes access out of a man-made box much
easier. These are made with sharp exterior wood screws that you can
install without drilling if the birds are already in the box. Quick,
easy and effective. Note that these perches are plain uncoated and
unpainted to provide the best footing for your birds. Also note that
these are not
recommended for the outside of your boxes. However these work great as
interior perches in all locations. My bluebirds love these and use them
all the time. Installed inside the box this perch allows the female bird
to sit comfortably further inside the box and still peer out for
dangers. Sitting in the hole itself means the bird is farther out in the
nest box hole and more vulnerable. Also of course the inner perch allows
easy access for the chicks to fledge. Lastly the perch allows the
parents to hang on and reach down to inspect and feed the babies.

See videos below:

When
feeding the young the parents can reach down further into the box without
landing on the nest. This is especially useful if you have a full box of
mature fledglings. It also gives the female a comfortable perch inside where
she can still peer outside for long periods of time. Lastly of course the
inner perch gives the chicks easy access to the hole when they are ready to
fledge.

Note: In the video
it states that the horizontal dowel is 1/4 inch. I have upgraded this kit to
3/8 inch since it is stronger and better. Kit includes everything you see
plus instructions. See photos below:

Box NOT included.

This next video
shows the female bluebird using the inner perch to reach down from above to
inspect her babies. Skip to about the 3:15 mark to see her use the perch in
this manner.